In the field of automatic machining, assembly, and other forms of workpiece processing, it is customary practice to use transfer machines which employ a multiplicity of stations which operate sequentially on a given workpiece, with a line of workpieces progressively transferred along the line of stations, by an automatic transfer mechanism.
For illustrative purposes, and by way of example, there exist in industry transfer lines for machining the cylinder heads for internal combustion engines, referred to as head lines. The total number of individual stations in such a head line may exceed 100. It will be understood that each station performs a given operation on each head (workpiece), and, at the end of a given cycle, the heads are indexed forward one station increment; and when a head is discharged from the line, all operations will have been performed on it.
Building such a line as a single transfer machine creates two significant problems: the first is the practical problem of building a transfer system capable of accurately and reliably transferring such a large number of heavy workpieces along a single transfer machine. The second concerns the likelihood of downtime. If a single station of a transfer machine is down or inoperative for a variety of reasons, among which are broken or dull tools, electrical, hydraulic, or mechanical malfunction, then the entire line, of which such a down station is a part, is down or nonoperative as a result. This situation has long been recognized in the industry, and, as a result, overall processing lines incorporating a large number of stations are generally subdivided into multiple sections which may range from 2 to 12 or more. Each such section is then operated as a single machine with its own independent transfer mechanism for transferring parts between its multiplicity of stations. Between such machine sections, there is generally incorporated an independent workpiece transfer system, which may be a roll conveyor, accumulating conveyor, power and free conveyor, monorail conveyor, and even manual labor, for transfer of the workpieces from the last station of the upstream section to the first station of the downstream section. In almost all cases, some degree of automatic or manual workpiece storage between sections is thereby achieved.
With some degree of workpiece storage between machine sections, it will be seen that when one station of a single section goes down, that entire section goes down, but the other sections may continue to operate for as long as there are workpieces stored in the between-section transfer system immediately downstream of the non-operative section and as long as there are spaces available in the between-section transfer system immediately upstream of the non-operative section.
As a broad generalization, the greater the amount of between-section transfer system storage capacity, the longer a given section may be down without causing the other sections to go down, and, as a second broad generalization, the larger the number of sections into which a given line is subdivided, the less likelihood a given section will be inoperative at any given time.
It is one objective of this invention to create a system of workpiece storage between sections which is more flexible, more economical, in terms of cost per part stored, and less wasteful of floor space than the systems presently in use.
In high production situations, it is not uncommon to find multiple parallel lines operating adjacent to one another in a given plant. Hypothesizing that there exist three parallel lines, A, B, and C, each of which is divided into six sections, 1, 2, 3, 4, 5, and 6, there arise many occasions in which, for example, section 1 of line A is down while at that same time, section 5 of line B is down, and at that same time, section 3 of line C is down. Under such conditions, it can be seen that with suitable cross-transferring between lines, the productivity of all three lines can be maintained at 2/3 of the theoretical full productivity of all three lines, even though each line, as a continuous system, is down. This technique of crossfeeding between corresponding "between-section" transfer systems of multiple parallel lines to maintain partial production when non-corresponding sections of multiple lines are simultaneously down has also long been known and utilized by industry.
It is a further object of this invention to create a storage system which, by its nature, provides a simple means to transfer workpieces between corresponding points of multiple parallel processing lines.
In the processing of many types of workpieces, there often exist sections of transfer lines which are significantly slower in operation than the remaining sections of that same transfer line. In such cases, it is common practice to utilize two parallel identical sections, each of which operates on approximately half of the workpieces as compared to the remaining sections of the line.
It is a further objective of this invention to provide a means of dividing the flow from a single section of a transfer line to a multiplicity of parallel substantially identical sections of a transfer line in addition to the storage function of this invention; and, conversely, to provide a means of recombining the outputs from a multiplicity of substantially identical sections of a transfer line into a single input to a subsequent section.
Other objectives and features of the invention will be apparent in the following description, claims, and accompanying drawings in which the principles of operation and use are set forth in connection with the best modes presently contemplated for the practice of the invention.